This application is a 371 of PCT/EP2016/077749 filed 15 Nov. 2016.
The disclosure relates to a blade for screens that are normally used to treat fibrous pulp suspensions. The blade can be secured to the rotor and has a leading edge and a trailing edge. A screen with blades is also disclosed.
A state-of-the-art screen for cleaning a fibrous pulp suspension is shown in FIG. 1. It has a rotor 1 and a screen basket 8. The rotor 1 rotates round the rotor axis 2. The sense of rotation of the rotor 1 is indicated by an arrow. Several blades 3 are bolted to the brackets 4 through fastening holes 7 at the rotor 1. Of course, it is also conceivable to secure the blades by welding. The spacing between the blades and the screen basket 8 is shown here as Y.
When viewed in a horizontal projection, the blades 3 have a straight leading edge 5 and a straight trailing edge 6. Their cross-section has a wing-shaped profile, but other shapes are also possible here and are also in use.
During operation, pressure and suction pulses as well as turbulence are generated by the blades 3 at the screen basket 8 perforation (holes or slots). This prevents the screen basket openings from being blocked. Due to generation of these pulses and turbulences, a screen consumes a lot of energy and is thus expensive to operate. Rotor blades with a curved leading edge are also known from EP2203590A1, WO2012084562A1, DE102009014810A1, EP1143065A2, U.S. Pat. No. 3,939,065A, DE69424661T2, WO9401618A1, CN104532652A and DE6012137T2. U.S. Pat. No. 3,939,065 A discloses a rotor body with elevations that have a curved leading edge and a slightly curved trailing edge. EP 1 143 065 A2 discloses a blade with straight leading and trailing edges that are slanted towards the rear.